1. Field of the Invention
This invention relates generally to machine tools, and more particularly to the spindle mount and drive and toolholder for a machine tool with automatic toolchanger.
2. Description of the Prior Art
The machine tool art is extensive. Vertical milling machines constitute a large component of the machine tool art. Typically they include a horizontally positionable table to hold tile workpiece, a tool (usually a cutter of some type) for treating tile workpiece, a powered rotating spindle for rotating the tool and vertically drivable by hand or power to advance the tool into the workpiece. More recent machines are controlled by computer and, due to their versatility, are commonly referred to as computer numerically controlled, or CNC, machining centers. They are usually equipped with some kind of automatic tool changing feature to enable the machine to make different types, sizes and contours of cuts, some of them including means for translating the workpiece mounting table or the spindle on horizontal axes automatically for contouring.
A machining center having such features is shown and described in U.S. Pat. No. 4,443,929 issued Apr. 24, 1984 to me and Walter Breitkopf. It uses an automatic tool changing feature as disclosed in more detail in U.S. Pat. No. 3,999,769 issued Dec. 28, 1976 to me and Walter Breitkopf, and which, for some features, refers to our earlier U.S. Pat. No. 3,797,956 issued Mar. 19, 1974. In that system, and referring to the reference numerals in tile earlier U.S. Pat. No. 3,999,769, toolholders 58 were removably mounted in retaining rings 48 mounted in a rotatable turret plate 44 which could be indexed to place the axis of any one of the toolholders in line with a coupling plug 36 at the bottom of the tool drive spindle 30. When the turret plate was rotated to place the desired toolholder directly under and in axial alignment with the spindle, the spindle was driven downward by the spindle mounting sleeve 24 in FIG. 2 of that patent for engagement of tile coupling plug 36 on the spindle with the toolholder. Further downward drive of the spindle drove the toolholder out of the turret plate and into position to engage the cutting tool therein (not shown) with the workpiece. The spindle drive motor was energized to rotate the spindle for the cutting operation, while the sleeve 24 did not rotate. The purpose of the sleeve was to contain and rotatably support the spindle and drive the spindle up and down in the housing 22. When the machining with the cutter in that toolholder was complete, the spindle sleeve was retracted and, when the plug had been pulled up to the position shown in FIG. 2, the toolholder was released into and secured in the retaining ring 48 in the turret disk. Then the turret plate 44 could be rotatably indexed to place the next desired toolholder in position under the spindle whereupon the spindle would be driven downward to connect it to the toolholder and drive the toolholder and associated tool out of the disk to engage the tool with the workpiece. The disclosures of the above-mentioned patents are incorporated herein by reference.
In machine tools, it is generally desirable to have a high degree of rigidity so that the surface which is treated (usually by cutting) on the workpiece is well within acceptable tolerance. Cutting forces transverse to the rotational axis of the tool tend to cause a bending moment from the cutter to the spindle support. The result is a certain amount of radial deflection of the spindle caused by the cutting forces. To improve rigidity of a spindle within dimensional constraints of a machine structure, and still avoid the necessity of the spindle housing bodily moving toward and away from the turret plate and the workpiece, an improved spindle mounting, rotating and driving combination was invented and is shown and described in U.S. Pat. No. 5,242,360 issued Sep. 7, 1993, the disclosure of which is incorporated herein by reference. But there is an effort by some people in the machine tool industry, particularly the German national standards institute (the DIN) to standardize on a hollow-shank, short-taper toolholder for use on machine tools worldwide. The toolholder is referred to as the DIN HSK standard toolholder. The present invention is addressed to achieving the benefits of the structure of the aforementioned U.S. Pat. No. 5,242,360 but accommodating the HSK standard toolholders.